King Derby
refers to Elias Haskett Derby (1739-1799), son of Captain Richard Derby,
the maritime merchant who started the business that helped establish Salem
as an important center of maritime trade in the late eighteenth century.

Bryant F. Tolles, Jr., former executive director of the Essex Institute
and author of Architecture in Salem (1983) on the Derby House:

Similar
in form to the Crowninshield-Bentley House is the Derby House (168 Derby
St.), on the grounds of the Salem National Maritime Historic Site. The
oldest brick house in Salem, this striking two-and-one-half story Georgian
Colonial building was erected in 1761-62 by Captain Richard Derby for
his son Elias Haskett Derby and Elias's new wife, Elizabeth Crowninshield.
Over the next century other members of the city's leading merchant families
(Nichols, Prince, and Ropes) owned and occupied the house. It then fell
on hard times, but was rescued in 1927-28 by the Society for the Preservation
of New England Antiquities, partially restored under the direction of
George Francis Dow, and completed by the Park Service since [sic]1938.
Worthy of note is the superb brick detailing and the Tuscan Doric classical
doorway with triangular pediment above. The kitchen ell was added in
about 1790. Overlooking Salem Harbor, the Derby House, with its furnished,
richly paneled interior rooms, constitutes a major park of the Park
Service's riveting story of Salem's maritime heritage.

( From
"The Historic Architecture of Salem" by Bryant F. Tolles, Jr., pp. 66+
in Salem Cornerstones of a Historic City)